The present invention relates to an in-tank motordriven fuel pump adapted to be mounted in a fuel tank for an automobile or the like, and more particularly to a motordriven fuel pump improved in discharge efficiency.
FIG. 27 shows a conventional in-tank motor-driven fuel pump for an automobile or the like similar to a pump as disclosed in Japanese Utility Model Laid-Open Publication No. 58-151397. Referring to FIG. 27, reference numeral 8 generally designates a motor-driven fuel pump mounted in a fuel tank 2 and vertically supported by a bracket 4. The motor-driven fuel pump 8 is generally composed of a pump section and a motor section which are formed in a cylindrical housing 10. The pump section is located in a lower portion of the housing 10, while the motor section is located in an upper portion of the housing 10. The pump section is partitioned by a partition wall 14 from the motor section. An end plate 28 is fixedly engaged at a lower end of the housing 10. There is defined a space between the partition wall 14 and the end plate 28 for engaging therein an annular upper spacer 20, a disc-like intermediate plate 46 having a central hole, and an annular lower spacer 26. An upper impeller or a second-stage impeller 52 is rotatably received in an upper space defined by the partition wall 14, the upper spacer 20 and the intermediate plate 46. A lower impeller or a first-stage impeller 40 is rotatably received in a lower space defined by the intermediate plate 46, the lower spacer 26 and the end plate 28. The second-stage and first-stage impellers 52 and 40 are formed at their outer peripheries with a plurality of radial vanes 48 and 44, respectively, for effecting a pumping function. At a lower surface of the partition wall 14, both surfaces of the intermediate plate 46 and an upper surface of the end plate 28, there are provided annular grooves facing the radial vanes 44 and 48. First-stage annular pump chamber 30 is formed around the radial vanes 44, and second-stage annular pump chamber 18 is formed around the radial vanes 48. The end plate 28, the intermediate plate 46 and the partition wall 14 are formed with a fuel inlet 42, a communication passage 22 and a pump outlet 50, respectively, at such positions as to face the first-stage and second-stage pump chambers 30 and 18. The impellers 40 and 52 are axially slidably mounted at their central portions to a motor shaft 58 projecting downwardly through the partition wall 14 from an armature 56 of the motor section which has magnets 54, and are driven to be rotated by the motor section.
When the motor section is operated, the impellers 40 and 52 are rotated to suck the fuel in the fuel tank 2 from the fuel inlet 42. The fuel sucked is boosted in the first-stage and second-stage pump chambers 30 and 18, and is fed through the pump outlet 50 into a motor chamber 12. The fuel in the motor chamber 12 is then discharged from a fuel discharge outlet 6.
In the motor-driven fuel pump as mentioned above, there are formed a sealing portion 16 between the partition wall 14 and the second-stage impeller 52, a sealing portion 24 between the second-stage impeller 52 and the intermediate plate 46, a sealing portion 32 between the intermediate plate 46 and the first-stage impeller 40 and a sealing portion 34 between the first-stage impeller 40 and the end plate 28. There are defined clearances in the sealing portions 16, 24, 32 and 34 to cause a fuel leakage loss. That is, the fuel leaks through the clearances of the sealing portions 16, 24, 32 and 34 between the pump chambers 18, 30 and a fuel well 36 through communication holes 38. To prevent a reduction in pump discharge efficiency due to the leakage loss, the clearances are made greatly small. Accordingly, if the dimensional accuracy of the sealing portions 16, 24, 32 and 34 is low and the impellers 40 and 52 have small unbalance, the impellers 40 and 52 under rotation generate an increased frictional resistance at the sealing portions 16, 24, 32 and 34. As a result, the rotation of the motor is reduced to cause a reduction in discharge efficiency of the motor-driven fuel pump 8.